Cartons, trays and other folding containers having end panel locking structures are known in the art. Particularly, the end walls of the carton are formed by overlapping end wall panels articulated to the side and bottom walls of the carton body and locked together with tongues, tabs and slits or the like. Boxes and cartons of this type are used to package a wide range of goods from, for example, cookies to automobile parts.
U.S. Pat. No. 1,425,256 to Hickman et al discloses a berry container having an end panel locking structure. Overlapping end panels articulated to the carton sidewalls include a cooperating tab and slit structure providing locking action. A third, solid interior end panel articulated to the bottom wall provides increased strength to the carton.
While the Hickman concept provides a strong and secure carton, it is not without its disadvantages. The Hickman carton is not designed for erection on the high speed carton forming and erecting machinery required to be economically competitive in the marketplace of today. Specifically, the solid interior end panel can sometimes provide a hinderance to secure engagement of the end lock. It has been found that the solid interior end panel resists proper overtravel of the locking tab as it is punched into position by the punch-in finger of the erecting machinery. Without complete engagement of the locking tab in the cooperating slit being assured, consistent carton erection cannot be obtained.
U.S. Pat. No. 3,206,098 to Stenger et al provides a portion of the locking structure of the overlapping end panels extending above the upper limit of the solid interior end panel. This structure allows some relief and flexibility to aid in lock engagement.
The Stenger carton, however, suffers from several disadvantages. The lock structure is complicated and often interferes with product loading and/or smooth operation of the hinged carton top. The upper edge portion of the lock presents a jagged edge that can hang on the product as it is being inserted, or catch the lower edge of the charlotte flaps on the top as the carton is being closed. Further, since the interior end panel does not extend along the entire depth, it does not provide the desired degree of isolation of the carton contents from outside elements as, for example, when packaging semi-exposed food products, such as butter patties.
A need is, therefore, identified for a carton with an improved thread and punch lock on the overlapping end panels.